1. Field of the Invention
The present invention relates to a z-stage configuration and application thereof, and more especially, to a z-stage configuration for a scanning electron microscope (SEM) machine, a system for detecting a surface movement of a specimen on the z-stage, and a system for offsetting the SEM vibration.
2. Background of the Related Art
In a SEM machine, a stage is used to carry a specimen for imaging or inspection. The stage includes an x-y stage, a z stage on the x-y stage and an E-chuck structure on the z stage, wherein the x-y stage is used to adjust the lateral position of the specimen, and the z-stage is used to adjust the height of the specimen for focus of an E-beam, the topography of the specimen, or the declined x-y stage.
FIG. 1 illustrates a cross-sectional view of the conventional z-stage structure and the structural relationship to the E-chuck structure. As shown in FIG. 1, the z-stage structure 10 includes a first metal plate 12, a second metal plate 14 and a third metal plate 16. A plurality of C-shape flex clamps 18 clamping a piezo actuator 181 are respectively configured on the four corners of the first metal plate 12 and against the second metal plate 14. A plurality of ceramic stands 20 between the second metal plate 14 and the third metal plate 16 are used to support the third metal plate 16 and electrically isolate the second metal plate 14 from the third metal plate 16, to which a high electrical voltage is applied. The E-chuck structure 22 is placed on the third metal plate 16 where the specimen (not shown) is attached to, and an EM shielding 24 supported by a plurality of stands 26 on the third metal plate 16 is around the E-chuck structure 22.
Further, referring to FIG. 1 and FIG. 2 simultaneously, a plurality of the optical mirror stands 28 are fastened on the two sides of the second metal plate 14. Two mirrors 30 are supported by the optical mirror stands 28 by means of glue or mechanical fastening and joining, and arranged on the two sides of the second metal plate 14. Two Laser interferometers 32 are arranged respectively near the two mirrors 30 to detect the vertical movement of the second metal plate 14 and then to send signals to a controller 34, such that an E-beam column 36 may receive a real-time location of the specimen.
However, the location of the optical mirror 30 and E-chuck structure 22 may have vibration deviation due to high frequency (about 200 Hz) of movement. The vibration deviation may cause the z-stage structure 10 to decline and signals detected by the Laser interferometer 32 to contain errors.